What is the Calvin Cycle?

The Calvin Cycle is primarily known as a process that produces high-energy sugars from the energy carriers ATP and NADPH generated during the light-dependent reactions of photosynthesis. This cycle occurs in the stroma of chloroplasts and involves the fixation of carbon dioxide into organic molecules.

During the Calvin Cycle, carbon dioxide is incorporated into a five-carbon sugar, ribulose bisphosphate (RuBP), through the action of the enzyme RuBisCO. The resulting six-carbon compound is unstable and quickly splits into two molecules of 3-phosphoglycerate (3-PGA). These molecules are then phosphorylated using ATP and reduced using NADPH, ultimately leading to the production of glyceraldehyde-3-phosphate (G3P), a three-carbon sugar. Some of the G3P molecules exit the cycle and can be used to form glucose and other carbohydrates, which serve as energy sources for the plant.

The other options describe different aspects of photosynthesis. The light-dependent reactions occur in the thylakoid membranes and are responsible for capturing energy from sunlight and converting it into chemical energy in the form of ATP and NADPH. While light energy is indeed converted to chemical energy, this description pertains more to the initial phase of photosynthesis rather than the